Clock generator circuit

ABSTRACT

A clock generator circuit for generating two pairs of clock signals comprises a NAND circuit and a NOR circuit cross-coupled to each other and each having an input for receiving a reference clock signal (φ 0 ). A first inverter is provided between the output of the NAND circuit and the other input of the NOR circuit, and a second inverter is provided between the output of the NOR circuit and the other input of the NAND circuit. A pair of clock signals (φ 2 , φ 2 ) are generated from the NAND circuit and the first inverter, while another pair of clock signals (φ 1 , φ 1 ) are generated from the NOR circuit and the second inverter.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a clock generator circuit for generating two pairs of clock signals by using a reference clock signal.

As the case may require, four clock signals, that is, two pairs of clock signals are used. For example, such clock signals are used in a switched cpacitor integrator. In this case, it is necessary that a pair of clock signals opposite in phase to each other are not overlapped with another pair of clock signals opposite in phase to each other.

2. Description of the Prior Art

One conventional clock generator circuit comprises a pair of NOR circuits cross-coupled to each other, which serve as an R-S flip-flop. This clock generator circuit generates two non-overlapping clock signals φ₁ and φ₂ opposite in phase to each other. (See: Electronics, page 99, Jan. 20, 1977.) In this circuit, when an inverter is connected to the output terminal of each of the NOR circuits, two inverted clock signals φ₁ and φ₂ of the clock signals φ₁ and φ₂ are also obtained. Thus, the clock generator circuit associated with such inverters generates two pairs of clock signals φ₁ and φ₁, and φ₂ and φ₂.

However, in the above-mentioned circuit, due to fluctuation in manufacture, the delay time of each of the inverters is fluctuated. At worst, this delay time is so long that the clock signal φ₁ may be overlapped with the clock signals φ₂ and φ₂ and in addition, the clock signal φ₂ may be overlapped with the clock signal φ₁ and φ₁.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide a clock generator circuit for generating two pairs of clock signals in which a pair of clock signals are surely non-overlapped with the other pair of clock signals.

According to the present invention, there is provided a clock generator circuit for generating two pairs of clock signals by using a reference clock signal, comprising: first and second logic circuits, each having first and second input terminals and an output terminal, for generating first and second clock signals, respectively, the first input terminal of each of the first and second logic circuits receiving the reference clock signal; a first delay circuit, connected between the output terminal of the first logic circuit and the the second input terminal of the second logic circuit, for delaying and inverting the first clock signal so as to generate a third clock signal which forms a pair with the first clock signal; a second delay circuit, connected between the output terminal of the second logic circuit and the second input terminal of the first logic circuit, for delaying and inverting the second clock signal so as to generate a fourth clock signal which forms a pair with the second clock signal; the first logic circuit detecting a change of the potential of the fourth clock signal so as to change the potential of the first clock signal, when the potential of the reference clock signal is high; and the second logic circuit detecting a change of the potential of the third clock signal so as to change the potential of the second clock signal, when the potential of the reference clock is low.

The present invention will be more clearly understood from the description as set forth below contrasting the present invention with the conventional circuit and with reference to the accompanying drawings, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram illustrating a general switched capacitor integrator;

FIGS. 2A through 2D are timing diagrams showing the signals appearing in the circuit of FIG. 1;

FIG. 3 is a logic circuit diagram illustrating one conventional clock generator circuit;

FIGS. 4A through 4F are timing diagrams showing the signals appearing in the circuit of FIG. 3;

FIG. 5 is a logic circuit diagram illustrating an embodiment of the clock generator circuit according to the present invention;

FIGS. 6A through 6E are timing diagrams showing the signals appearing in the circuit of FIG. 5;

FIG. 7 is a logic circuit diagram illustrating another embodiment of the clock generator circuit according to the present invention; and

FIGS. 8A through 8G are timing diagrams showing the signals appearing in the circuit of FIG. 7.

In FIG. 1, which illustrates a general switched capacitor integrator, SW₁ and SW₂ are switches; C₁ and C₂ are capacitors; and OP is an operational amplifier. In this case, the capacitor C₂ forms a negative feedback path of the operational amplifier OP. When the switch SW₁ is turned on, the capacitor C₁ is charged by an input voltage V_(in). After that, at the next timing, the switch SW₁ is turned off and, in turn, the switch SW₂ is turned on. As a result, the charges stored in the capacitor C₁ are moved to the capacitor C₂. Since the operational amplifier OP operates so as to hold its input terminal (-) at the ground level, an output voltage V_(out) appears in accordance with the quantity of the charges stored in the capacitor C₁.

The input voltage V_(in) is sampled by repeating the above-mentioned operation at a frequency of, for example, 128 kHz, so that the output voltage V_(out), corresponding to an integrated value of the sampled voltages, is obtained.

In FIG. 1, each of the switches SW₁ and SW₂ comprises a CMOS (Complementary MOS) circuit formed by a p-channel type transistor and a n-channel type transistor. Therefore, when the potential of a clock signal φ₁ and the potential of its inverted signal φ₁ are high and low, respectively, the switch SW₁ is turned on, while, when the potential of each of the signals φ₁ and φ₁ are low and high, respectively, the switch SW₁ is turned off. Similarly, when the potential of a clock signal φ₂ and the potential of its inverted signal φ₂ are high and low, respectively, the switch SW₂ is turned on, while, when the potential of each of the signals φ₂ and φ₂ are low and high, respectively, the switch SW₂ is turned off.

It should be noted that the switches SW₁ and SW₂ should not be simultaneously turned on. If the switches SW₁ and SW₂ are simultaneously turned on, the capacitor C₂ is charged directly by the input voltage V_(in) and as a result, a normal integration operation can not be performed.

FIGS. 2A through 2D are timing diagrams showing the signals appearing in the circuit of FIG. 1. As illustrated in FIGS. 2A through 2D, in order to prevent the switches SW₁ and SW₂ (FIG. 1) from being turned on simultaneously, a pair of the clock signals φ₁ and φ₁ are non-overlapped with the other pair of the clock signals φ₂ and φ₂. In more detail, the high potential of the clock signal φ₁ is non-overlapped with the high potential of the clock signal φ₂ and the low potential of the clock signal φ₂. In addition, the low potential of the clock signal φ₁ is non-overlapped with the high potential of the clock signal φ₂ and the low potential of the clock signal φ₂.

FIG. 3 is a logic circuit diagram illustrating one conventional clock generator circuit. As illustrated in FIG. 3, the clock generator circuit comprises two NOR circuits 31 and 32 cross-coupled to each other which serve as an R-S flip-flop. (See: Electronics, page 99, Jan. 20, 1977.) The NOR circuit 31 receives a reference clock signal φ₀ directly, while the NOR circuit 32 receives the reference clock signal φ₀ via an inverter 33. Each of the NOR circuits 31 generates clock signals φ₁ and φ₂, respectively, and in addition, clock signals φ₁ and φ₂ are obtained by inverting the clock signals φ₁ and φ₂, respectively. For this purpose, two inverters 34 and 35 are provided. Thus, two pairs of clock signals φ₁ and φ₁, and φ₂ and φ₂ are obtained.

FIGS. 4A through 4F are timing diagrams showing the signals in the circuit of FIG. 3. Referring to FIGS. 4A through 4F, the operation of the circuit of FIG. 3 will now be explained. At a time t₁, the potential of the reference clock signal φ₀ is changed from low to high, as illustrated in FIG. 4A and, in turn, at a time t₂, the potential of a signal φ₀ is changed from high to low, as illustrated in FIG. 4B. In this state, since the potential at an input terminal 31-B of the NOR circuit 31, which is the same as the potential of the clock signal φ₂ as illustrated in FIG. 4E, remains low, the NOR circuit 31 detects the change of the potential at an input terminal 31-A thereof, so that, at a time t₃, the potential of the clock signal φ₁ is changed from high to low, as illustrated in FIG. 4C and, in turn, at a time t₄, the potential of the clock signal φ₁ is changed from low to high, as illustrated in FIG. 4D. In addition, in this state, since the potential at an input terminal 32-A of the NOR circuit 32, which is the same as the potential of the signal φ₀ as illustrated in FIG. 4B, remains low, the NOR circuit 32 detects the change of the potential at an input terminal 32-B thereof, so that, at a time t₅, the potential of the clock signal φ₂ is changed from low to high, as illustrated in FIG. 4E and, in turn, at a time t₆, the potential of the clock signal φ₂ is changed from high to low, as illustrated in FIG. 4F.

As illustrated in FIGS. 4C, 4E and 4F, the high potential of the clock signal φ₁ is never overlapped with the high potential of the clock signal φ₂ and the low potential of the clock signal φ₂. Contrary to this, with regard to the clock signal φ₁, as illustrated in FIGS. 4D, 4E and 4F, if τ₁ >τ₂ where τ₁ is a delay time of the inverter 34 and τ₂ is a delay time of the NOR circuit 32, the low potential of the clock signal φ₁ is overlapped with the high potential of the clock singal φ₂. In addition, if τ₁ >τ₂ +τ₃ where τ₃ is a delay time of the inverter 35, the low potential φ₁ is also overlapped with the low potential of the clock signal φ₂.

Similarly, when the potential of the reference clock signal φ₀ is changed from high to low, as illustrated in FIGS. 4C, 4D and 4E, the high potential of the clock signal φ₂ is never overlapped with the high potential of the clock signal φ₁ and the low potential of the clock signal φ₁. Contrary to this, with regard to the clock signal φ₂, as illustrated in FIGS. 4C, 4D and 4F, if τ₃ >τ₄ where τ₄ is a delay time of the NOR circuit 31, the low potential of the clock signal φ₂ is overlapped with the high potential of the clock signal φ₁. In addition, if τ₃ >τ₄ +τ₁, the low potential of the clock signal φ₂ is overlapped with the low potential of the clock signal φ₁.

However, the delay time τ₁ of the inverter circuit 34 and the delay time τ₃ of the inverter 35 are often variations due to fluctuation in manufacture. Accordingly, it may happen that τ₁ >τ₂ (or τ₂ +τ₃) or τ₃ >τ₄ (or τ₄ +τ₁) is satisfied. Thus, in the circuit of FIG. 3, the clock signals φ₁ and φ₁ may be overlapped with the clock signals φ₂ and φ₂.

FIG. 5 is a logic circuit diagram illustrating an embodiment of the clock generator circuit according to the present invention. As illustrated in FIG. 5, the clock generator circuit comprises a NAND circuit 51 and a NOR circuit 52 cross-coupled to each other, and two inverters 53 and 54. A reference clock signal φ₀ is supplied commonly to an input terminal 51-A of the NAND circuit 51 and an input terminal 52-A of the NOR circuit 52. The NOR circuit 52 generates a clock signal φ₁ and in turn, the inverter 54 generates a clock signal φ₁ which forms a pair with the clock signal φ₁, while the NAND circuit 51 generates a clock signal φ₂ and in turn, the inverter 53 generates a clock signal φ₂ which forms a pair with the clock signal φ₂. Thus, two pairs of the clock signals φ₁ and φ₁, φ₂ and φ₂ are obtained.

FIGS. 6A through 6E are timing diagrams showing the signals appearing in the circuit of FIG. 5. Referring to FIGS. 6A through 6E, the operation of the circuit of FIG. 5 will now be explained. At a time t₁, the potential of the reference clock signal φ₀ is changed from low to high, as illustrated in FIG. 6A. In this state, since the potential at the input terminal of the NOR circuit 52 remains low, the NOR circuit 52 detects the change of the potential at the input terminal 52-A so that, at a time t₂, the potential of the clock signal φ₁ is changed from high to low as illustrated in FIG. 6B and in turn, at a time t₃, the potential of the clock signal φ₁ is changed from low to high as illustrated in FIG. 6C. In addition, in this state, since the potential at the input terminal 51-A of the NAND circuit 51, which is the same as the potential of the reference clock signal φ₀, remains high as illustrated in FIG. 6A, the NAND circuit 51 detects the change of the potential at the input terminal 51-B so that, at a time t₄, the potential of the clock signal φ₂ is changed from high to low as illustrated in FIG. 6E and, in turn, the potential of the clock signal φ₂ is changed from low to high as illustrated in FIG. 6D.

As illustrated in FIGS. 6B, 6D and 6E, since the rise of the potential of the clock signal φ₂ and the fall of the potential of the clock signal φ₂ follow the fall of the potential of the clock signal φ₁, the high potential of the clock signal φ₁ is never overlapped with the high potential of the clock signal φ₂ and the low potential of the clock signal φ₂. In addition, as illustated in FIGS. 6C, 6D and 6E, since the rise of the potential of the clock signal φ₂ and the fall of the potential of the clock signal φ₂ follow the rise of the potential of the clock signal φ₁, the low potential of the clock signal φ₁ is never overlapped with the high potential of the clock signal φ₂ and the low potential of the clock signal φ₂.

On the other hand, at a time t₆, the potential of the reference clock signal φ₀ falls as illustrated in FIG. 6A and after that, at a time t₇, the potential of the clock signal φ₂ rises as illustrated in FIG. 6E. And, in turn, at a time t₈, the potential of the clock signal φ₂ falls as illustrated in FIG. 6D. After that, at a time t₉, the potential of the clock signal φ₁ rises as illustrated in FIG. 6B and, in turn, at a time t₁₀, the potential of the clock signal φ₁ falls as illustrated in FIG. 6C. Therefore, the high potential of the clock signal φ₂ is never overlapped with the high potential of the clock signal φ₁ and the low potential of the clock signal φ₁ and, in addition, the low potential of the clock signal φ₂ is never overlapped with the high potential of the clock signal φ₁ and the low potential of the clock signal φ₁.

FIG. 7 is a logic circuit diagram illustrating another embodiment of the clock generator circuit according to the present invention. In FIG. 7, inverters 61 through 68 are added to FIG. 5. The operation of the circuit of FIG. 7 is similar to that of the circuit of FIG. 5.

FIGS. 8A through 8G are timing diagrams showing the signals appearing in the circuit of FIG. 7. Referring to FIGS. 8A through 8G, the operation of the circuit of FIG. 7 will now be explained. At a time t₁, the potential of the reference clock signal φ₀ rises as illustrated in FIG. 8A. After that, at a time t₂, the potential of a signal φ_(A) generated from the NOR circuit 52 falls, as illustrated in FIG. 8B. As a result, at a time t₃, the potential of the clock signal φ₁ falls as illustrated in FIG. 8C and, in turn, at a time t₄, the potential of the clock signal φ₁ rises as illustrated in FIG. 8D. After the rise of the clock signal φ₁, at a time t₅, the potential of the signal φ_(B) generated from the NAND circuit 51 falls. As a result, at a time t₆, the potential of the clock signal φ₂ falls as illustrated in FIG. 8G and, in turn, at a time t₇, the potential of the clock signal φ₂ rises as illustrated in FIG. 8F.

As illustrated in FIGS. 8D, 8F and 8G, since the rise of the potential of the clock signal φ₂ and the fall of the potential of the clock signal φ₂ follow the rise of the potential of the clock signal φ₁, the low potential of the clock signal φ₁ is never overlapped with the high potential of the clock signal φ₂ and the low potential of the clock signal φ₂.

In order to prevent the high potential of the clock signal φ₁ from being overlapped with the high potential of the clock signal φ₂ and the low potential of the clock signal φ₂, the following condition should be satisfied:

    τ.sub.11 >τ.sub.12 and τ.sub.11 >τ.sub.13  (1)

where τ₁₁ is the total delay time of the inverters 67 and 68; τ₁₂ is the total delay time of the inverters 54, 65, 66, the NAND circuit 51 and the inverters 53, 61 and 62; and τ₁₃ is the total delay time of the inverters 54, 65, 66, the NAND circuit 51 and the inverters 63 and 64.

On the other hand, at a time t₈, the potential of the reference clock signal φ₀ falls as illustrated in FIG. 8A. After that, at a time t₉, the potential of the signal φ_(B) rises as illustrated in FIG. 8E. As a result, at a time t₁₀, the potential of the clock signal φ₂ rises as illustrated in FIG. 8G and, in turn, at a time t₁₁, the potential of the clock signal φ₂ falls as illustrated in FIG. 8F. After the fall of the potential of the clock signal φ₂, at a time t₁₂, the potential of the signal φ_(A) rises as illustrated in FIG. 8B. As a result, at a time t₁₃, the potential of the clock signal φ₁ rises as illustrated in FIG. 8C and, in turn, at a time t₁₄, the potential of the clock signal φ₁ falls as illustrated in FIG. 8D.

As illustrated in FIGS. 8C, 8D and 8F, since the rise of the potential of the clock signal φ₁ and the fall of the potential of the clock signal φ₁ follow the fall of the potential of the clock signal φ₂, the high potential of the clock signal φ₂ is never overlapped with the high potential of the clock signal φ₁ and the low potential of the clock signal φ₁.

In order to prevent the low potential of the clock signal φ₂ from being overlapped with the high potential of the clock signal φ₁ and the low potential of the clock signal φ₁, the following condition should be satisfied:

    τ.sub.14 >τ.sub.15 and τ.sub.14 >τ.sub.16  (2)

where τ₁₄ is the total delay of the inverters 63 and 64; τ₁₅ is the total delay time of the inverters 53, 61 and 62, the NOR circuit 52 and the inverters 67 and 68; and τ₁₆ is the total delay time of the inverters 53, 61 and 62, the NOR circuit 52 and the inverters 54, 65 and 66.

Note that the above-mentioned conditions (1) and (2) can be easily attained.

As explained hereinbefore, the clock generator circuit for generating two pairs of clock signals according to the present invention has an advantage in that a pair of clock signals are not overlapped with another pair of clock signals. Therefore, when the clock signals obtained by the clock generator circuit according to the present invention are applied to the switches SW₁ and SW₂ of the switched capacitor integrator of FIG. 1, the switched capacitor integrator can perform a reliable integration operation. 

We claim:
 1. A clock generator circuit for generating two pairs of clock signals by using a reference clock signal, comprising:first and second logic circuits, each having first and second input terminals and an output terminal, for generating first and second clock signals, respectively, the first input terminal of each of said first and second logic circuits receiving said reference clock signal; a first delay circuit, connected between the output terminal of said first logic circuit and the second input terminal of said second logic circuit, for delaying and inverting said first clock signal so as to generate a third clock signal which forms a pair with said first clock signal; a second delay circuit, connected between the output terminal of said second logic circuit and the second input terminal of said first logic circuit, for delaying and inverting said second clock signal so as to generate a fourth clock signal which forms a pair with said second clock signal; said first logic circuit detecting a change of the potential of said fourth clock signal so as to change the potential of said first clock signal, when the potential of said reference clock signal is high; and said second logic circuit detecting a change of the potential of said third clock signal so as to change the potential of said second clock signal, when the potential of said reference clock is low.
 2. A clock generator circuit as set forth in claim 1, wherein said first and second logic circuits are a NAND circuit and a NOR circuit, respectively.
 3. A clock generator circuit as set forth in claim 1, further comprising:a third delay circuit, connected to the output terminal of said first logic circuit, for delaying said first clock signal; a fourth delay circuit, connected to the output terminal of said second logic circuit, for delaying said second clock signal, the delay time of said third delay circuit being less than the total delay time of said first delay circuit, said second logic circuit and said second delay circuit and being less than the total delay time of said first delay circuit, said second logic circuit and said fourth delay circuit; and the delay time of said fourth delay circuit being less than the total delay time of said second delay circuit, said first logic circuit and said first delay circuit and being less than the total delay time of said second delay circuit, said first logic circuit and said third delay circuit. 